Installation layout for two coaxial shaft lines

ABSTRACT

In a layout with two concentric shaft lines ( 15, 16 ), one of which projects beyond the other, a seal support sleeve ( 38 ) placed between them has a conical shape and bears on a spacer ( 40 ) of the external shaft line, so that an assembly nut ( 19 ) of the forward end is accessible from the back passing through the space ( 43 ) between the two shaft lines ( 15, 16 ), so that the nut can be unscrewed and the external shaft line can be disassembled.  
     The invention may be applicable to front bearings of gas turbine high pressure shaft lines and makes it possible to disassemble the high pressure body from behind, without needing to disassemble equipment such as a fan on the front of the machine. This does not hinder the installation of a movement control gear ( 20 ).

The purpose of this invention is a layout for the installation of twocoaxial shaft lines and particularly a so-called low pressure shaft lineas shown in FIG. 1 connecting the low pressure compressor 1 to the lowpressure turbine 2 in a gas turbine, surrounded by a high pressure shaftline connecting the high pressure compressor 3 to the high pressureturbine 4.

In this type of machine, the internal shaft line 15 (low pressure)projects beyond the front of the external shaft line 16 (high pressure)and can finish at a shaft end 5 supporting a large volume fan 6 on whichlarge radius blades are fitted to discharge air into an auxiliary stream7 surrounding the main gas stream 8, and if there is an accidentalbreakage in this fan, there will be a severe out-of-balance mass on theinternal shaft line 15. Thus, some arrangements need to be made.Firstly, a bearing 9 called the number 1 bearing right at the front ofthe internal shaft line 15 may be made fusible or breakable, in otherwords it may be installed on a low resistance support 10 that breaks assoon as an out-of-balance mass develops, so that the resulting largeforces that are then generated are not transmitted to the rest of thestator structure. The shaft end 5 is then free to tilt by moving underthe effect of the out-of-balance mass until the assembly that it formswith the fan 6 moves into a new position in equilibrium in rotation andwithout necessarily causing any further damage until the machine stops.The shaft end 5 makes this movement tilting around a so-called bearingnumber 2 behind the previous bearing, that supports its back end and amain shaft in the internal shaft line 15. This bearing is denotedreference 17. It thus controls the axial position of the internal shaftline 15.

A movement control gear 20, designed particularly to start the machineand activated by a transmission shaft 25 perpendicular to the shaftlines 15 and 16, must be placed between this bearing 17 and a so-calledbearing number 3 (reference 18) that provides support to the forward endof the external shaft line 16. The previous shaft bearing 17, being asfar backwards as possible to improve the dynamic resistance of theinternal shaft line 15, is only separated from it by just sufficientspace to contain the gear 20. An assembly nut is screwed around theforward end of the external shaft line 16 to hold it in place againstthis bearing 18 by stopping in contact on the bearing. This nut, thatextends forwards from the bearing 18 and on the movement control gear20, is difficult to access, particularly because a seal support sleevemust be placed behind the bearing 17 immediately in front of the nut,overlapping the forward end of the external shaft line 16 and a portionof the internal shaft line 15 to create a seal between them. Disassemblyof the high pressure shaft line 16, before maintenance, is usually onlypossible after disassembling the machine in front of the nut, andparticularly the fan 6, so that it can be reached and unscrewed.

Refer to French patent 2 783 579 for a description of a layout by whichthe nut can be unscrewed from behind using a special tool inserted intothe annular space between the shaft lines, which is more convenientdespite the fact that this space is narrow since there is then no needfor any major disassembly of elements of the machine to be able toremove the high pressure shaft line; but the selected layout consists ofscrewing the nut in the external shaft line whereas it is conventionallyscrewed around the shaft line, which changes the entire design of theforward end of the shaft line and it can introduce other disadvantages.In this case, another solution is proposed to provide easy access to thenut holding the external shaft line 16 in place from behind withoutmaking any major change to the design; the narrow space around the nutmakes a few modifications to surrounding parts of the machine necessary,but it will be seen that they are mainly applicable to sealing andmovement control devices, for which the design is less restrictive.

In its most general form, the representative layout of the inventioncomprises coaxial internal and external shaft lines, a forward part ofthe internal shaft line projecting beyond a forward end of the externalshaft line, a sleeve surrounding the shaft lines and supporting a sealassociated with each of the shaft lines, a bearing supporting theexternal shaft line close to the forward end and a bearing retaining nutscrewed around the forward end, characterized in that it comprises aspacer with an adjustment part slid around the external shaft line andtightened between the nut and the bearing, and a sealing part arrangedaround the nut and on which the seal associated with the external shaftline rubs.

The advantages of this arrangement and other aspects of the inventionwill be discovered after reading the commentary on the followingfigures:

FIG. 1, already described, is an overview of a gas turbine;

FIG. 2 shows a layout prior to the invention and in which the problemsof access to the nut mentioned above were not solved;

FIG. 3 shows a layout conform with the invention; and

FIG. 4 shows a view of another layout conform with the invention.

FIG. 2 shows a portion of the internal shaft line 15, the forward end ofthe external shaft line 16, one end of the number 2 bearing 17, thenumber 3 bearing 18, the assembly nut 19 of bearing 18, the movementcontrol gear 20, a crown wheel 21 engaged with the gear 20 and retainedbetween the external shaft line 16, the nut 19 and the bearing 18 toparticipate in the assembly of the bearing 18 as a thrust bearing, theseal support sleeve 22, its two seals 23 and 24 rubbing on contiguousportions of shaft lines 15 and 16; and the environment of the gear 20comprises a transmission shaft 25 connected in rotation to the gear 20by splines 26 and engaged in a hub 27 of the gear 20; a pair of bearings28 and 29 engaged around the hub 27; a housing 30 connected by screwingto an extension 31 of the sleeve 22 and (at right in the figure) to acasing 32 of the stator; and a shell 33 screwed to the housing 30 thatretains the bearing 29 on the far end from gear 20, while the otherbearing 28 close to the gear 20 is driven by the hub 27 and slides inthe housing 30; collars 34 and 35 of the bearing 28 close to the gear 20and the shell 33 are applied in thrust on the housing 30 and are screwedto it to keep the bearings 28 and 29 in a fixed position along the hub27. The attachment screws are not shown to simplify the drawing. Themeans of retaining the bearings 28 and 29 include nuts, thrust washers,force fitted sleeves, in a known manner. In this case, the bearing 28 isa ball bearing and the other bearing 29 is a roller bearing, without aninternal ring and in which the rollers bear directly on the hub 27.

It is worthwhile mentioning the method of fitting the assembly onto thegear 20 after the nut 19 has been screwed into place. The gear 20, thebearing 28 adjacent to it and the housing 30 are installed by screwingthe housing onto the casing 32, and the shell 33 and the bearing 29 arethen installed by fixing the shell to the housing 30, and the sealsupport sleeve 22 is fixed to the housing 30 by sliding it backwards;finally the transmission shaft 25 is inserted in the hub 27. It is seenthat the nut 19, well surrounded by other parts, has become inaccessibleunless major disassembly operations are carried out. Since the seal 24rubs on a lip 14 of the external shaft line 16 that extends forwardsfrom the nut 19 and the nut is screwed around this shaft line 16, theseal support sleeve 22 completely separates the nut 19 from the annularspace 13 between the shaft lines 15 and 16.

FIG. 3 illustrates a first embodiment of the invention and firstly showsa modification to the seal support sleeve, which in this case isassigned reference 38 and which has a conical shape, the seal 39 on theside of the high pressure shaft line 16 now having a larger diameterthan the unchanged seal 23 on the side of the low pressure shaft line15; the seal 39 does not rub on the actual shaft line 16, but rather ona sealing contact surface 41 of a spacer 40 integrated into the highpressure shaft line 16 and being provided for this purpose with a thrustcontact surface 42 inserted on the said shaft line and compressed by thenut 19 between it and the crown wheel 21.

The result of this is that the sealing contact surface 41 and the sleeve38 surround the nut 19 instead of covering it at the front and thus itbecomes accessible from behind, using a tool with claws not shown thatcan be slid in the annular space 43 between the shaft lines 15 and 16,and in that the nut 19 is at the forward end of the shaft line 16, thelip 14 that it surrounded having been replaced by the sealing contactsurface 41. The reference 44 is assigned to a locking part of the nut 19that comprises crab teeth penetrating into the nut 19 and the externalshaft line 16 to prevent any relative rotation when it is put intoplace; it is in the form of a split ring and is made of an elasticmaterial so that it can be opened to put it into place.

Some arrangements may be proposed at the side of the gear 20 to adaptthe structure to modify the shape of the seal support sleeve 38; thereare the two bearings 28 and 29 of the hub support 27 of the gear 20, thehousing 30 fixed to the extension 31 of the seal support sleeve 38 andthe casing 32, but in this case the shell 33 is replaced by a differentshell 45 that extends around the two bearings 28 and 29, and stillsupports the thrust collar 35 forming the attachment to the housing 30.

The assembly is different from the assembly in FIG. 2. It is made byfixing the housing 30, and then consists of inserting the gear 20 fittedwith the bearing closest to it (in this case 29) into the housing 30,placing it on a thrust surface 50 at the bottom of the housing 30,sliding the seal support sleeve 38 above the gear 20 and fixing it tothe housing 30. The shell 45 fitted with the bearing on the remote sideof the gear 20 (in this case the ball bearing 28) is then inserted intothe reaming in the housing 30 and around the hub 27 and the bearing 29.The bearing 28 supports a spacer ring 51 that finally touches the otherbearing 29 during this movement, pushes it back and thus lifts the gear20. When the collar 35 stops in contact with the housing 30, the gear 20engages with the crown wheel 21. The transmission shaft 25 is finallyinstalled.

FIG. 4 represents a variant of this idea in which bearings 28 and 29occupy the same positions as in the previous design and in which theshell 33 is also used; but the thrust collar 34 of the bearing 28 placedon the edge of the housing 30 is replaced by a collar 46 placed underit, and the collar 35 of the shell 33 with which it is in contact. Theassembly is made approximately in the same way as before, except thatthe bearings 28 and 29 must both be put into place after the gear 20 hasbeen put into place in the housing 30.

The innovation of the assembly according to the invention can beexplained as follows. The only way to access the nut 19 from the front,which was the only possible way before, is to slide the seal supportsleeve 22 forwards, separating it from the housing 30. This movement tolift the seal support sleeve in the forward direction is no longeruseful with the invention, and it is even impossible since the flaredrear part of the seal support sleeve 38 would stop in contact with theteeth of the gear 20. Thus, it would also be a problem to assemble thehousing 30 if the seal support sleeve 38 were moved forwards, since itsraised front edge would be stopped in contact with the flared rear partof the housing. Therefore, an assembly was adopted in which the sealsupport sleeve 38 is pulled clear backwards during assembly of thehousing 30 and the gear 20; its attachment flange 47 stops in contactwith the housing 30 at the back, unlike the situation in the previouslayout. The assembly does not cause any difficulty provided that thegear 20 can be lowered to the bottom of the housing 30 so that it doesnot collide with the attachment flange 47 or other parts of the sealsupport sleeve 38 before it is in its final position, which is perfectlypossible if the bearing 28, which is a ball bearing designed to supportthe gear 20 in the vertical direction (or the radial direction in thegas turbine) is fixed to the housing 30 later after having been insertedbelow the housing, then lifting the gear 20.

The layout in FIG. 3 with a single shell 45 for the vertical supportbearing 28 of the gear 20 and the other bearing 29, installed free toslide in the vertical direction, is simpler and probably more rigid, butit makes it necessary to change over the conventional positions of thebearings, and assembly can be more complicated due to the larger size ofthe shell 45. This is why the more ordinary layout in FIG. 4, in whichthe main difference in the method of assembly of bearings 28 and 29 isthe position of the collar 46, has many merits.

1. Layout comprising a coaxial internal shaft line (15) and a coaxialexternal shaft line (16), a forward part (5) of the internal shaft line(15) projecting beyond the forward end of the external shaft line (16),a sleeve (38) surrounding the shaft lines and holding two seals (23,39), each associated with one of the shaft lines, a bearing (18)supporting the external shaft line near the forward end and a retainingnut (19) of the bearing, screwed around the forward end, characterizedin that it comprises a spacer (40) with an adjustment part (42) slidaround the external shaft line and clamped between the nut and thebearing, and a sealing part (41) arranged about the screen and on whichthe seal (39) associated with the external shaft line rubs.
 2. Layoutaccording to claim 1, comprising a movement control gear (20) arrangedunder the nut (19), the spacer (40) and the sleeve (38).
 3. Layoutaccording to claim 2, comprising a gear support housing (30) surroundingthe gear and a gear hub (27) holding the gear (20) in the verticaldirection, characterized in that the bearing (28) is installed bypassing it below the housing (30) and the seal support sleeve (38)comprises a housing attachment flange (47) that stops as it comes intocontact with the housing (30) from the back.
 4. Layout according toclaim 3, characterized in that it comprises a single shell (45) fixed tothe housing (30), in which the bearing (28) and a second bearing (29)sliding in the vertical direction, are installed.